Do you mean analogWrite? analogRead won't control the transistor. Also, the analog output is accomplished using PWM, which simulates analog using pulses. It won't actually control the current to the transistor base, but will "stutter" the current to the motor, making it run faster or slower.

We'll need some additional information.

1) What type of transistor are you using? 2) How is it connected (schematic)? 3) Let us see the code. Paste it in a reply, select it, and press the # button above to format it in a code block.

Pat.

There are 10 types of people in the world, those that understand binary, and those that don't.

Try disconnecting the control wire from the Arduino and connect the base lead (with a 1k or 2.2k resistor) to the Arduino 5v to see if the transistor is working. Also, double check the wiring- you might have the transistor connected backwards.

1. Always use a diode across the motor to protect your transistors and the Arduino from reverse high voltage spikes.2. Always use a resistor between the Arduino and the transistor base to protect the transistor.

The 127 is a Darlington PNP transistor. It's a different type - don't use that; you need an NPN like the 120, 121, or 122.

If its wired correctly, you might have a faulty transistor, or damaged it somehow.

There are 10 types of people in the world, those that understand binary, and those that don't.

Darlington transistors have much larger gain factors than other transistor types. The -122 has a gain of 1000+ as opposed to a 2N2222 that has a gain closer to 100. Buy a pack of small transistors from Radio Shack, or somewhere similar, and try it again. Pick up some diodes and 1k resistors too when you are there!

What you might be experiencing is the transistor amplifying noise. Disconnect the base lead again, but connect it to ground. That should stop the motor. If not, there is a different problem.

Pat.

There are 10 types of people in the world, those that understand binary, and those that don't.

Diodes are placed backwards across the leads of inductive devices to short circuit their reverse voltage spikes when they turn off.

The electric coil develops a strong magnetic field when it is energized. When turned off, the magnetic field converts back to electricity with a reverse polarity to what generated it. This reverse voltage can damage the electronics and needs to be stopped. The backwards diode short circuits this reverse voltage back into the coil and not to the electronics.

There are 10 types of people in the world, those that understand binary, and those that don't.